Cam shaft for internal combustion engine

ABSTRACT

A cam shaft for valve operation in an internal combustion engine comprises two shaft elements of which the first (101, 201) is disposed inside the second (102, 202) and can be moved relative thereto angularly and/or axially. First cam elements (107, 207) provided on the first shaft element have at least lobe portions which extend radially outwardly through slots in the second shaft element to provide a cam surface, while second cam elements are provided on the second shaft element. The first and/or the second shaft element may comprise a number of individual tubular sections joined to one another.

BACKGROUND TO THE INVENTION

1. Field of the Invention

This invention relates to a cam shaft for an internal combustion engine,the cam shaft comprising two shaft elements of which one is disposedinside the other and which are capable of limited angular and/or axialmovement relative to one another, so as to change the relationshipbetween first cam elements connected to one of the shaft elements andsecond cam elements connected to the other shaft element.

Such a cam shaft is used in an internal combustion engine, with theinlet valves of the engine operated by the cam elements connected to oneof the shaft elements and the exhaust valves of the engine operated bythe cam elements connected to one of the shaft elements and the exhaustvalves of the engine operated by the cam elements connected to the othershaft element, in order to obtain a variation in the overlap of theopening periods of the inlet and exhaust valves. It is known that for anengine operating under part load and low speed conditions, only a smalloverlap between the opening periods of the inlet and exhaust valves isdesirable, whilst at higher speeds, gas dynamics dictate that a greateroverlap is required. If the inlet valves and exhaust valves of an engineare operated by separate cam shafts, a change in the angularrelationship between the cam shafts can readily be achieved byrelatively simple measures, for example by operating on a driving beltby means of an adjusting device, to increase or decrease the operativelength of the belt between the two cam shafts. This expedient is not,however, applicable to a simple engine which does not have two separatecam shafts, and hence the provision for adjustment of the relationshipof the cams to one another, to give favourable engine performance atboth high and low speeds, has to be provided within a single cam shaft.

2. Description of Prior Art

A cam shaft including two shaft elements disposed one within the otheris disclosed in EP 0254058 A2. In this, cam elements associated with theinner shaft element have cylindrical bores which slide on the outersurface of the outer shaft element, and in the region of their basecircles have single radially extending fixing bolts which reach throughperipheral slots in the outer shaft element to connect to the innershaft element. This type of fixing can result in deformation of theinner shaft element in the region of the fixing bolts, when the cam isunder torque loading. Damage can result, and loss of exact control ofthe cam timing.

SUMMARY OF THE INVENTION

It is broadly the object of the present invention to provide a cam shaftof the type having inner and outer shaft elements, wherein a secure andangularly-true connection is provided between the inner shaft elementand its associated cams.

According to the present invention, we provide a cam shaft for valveoperation in an internal combustion engine, comprising a first shaftelement and a second shaft element; said first shaft element beingdisposed within the second shaft element and being movable relativethereto; said first shaft element being provided with first cam elementsof which at least lobe portions extend outwardly through slots in saidsecond shaft element, and said second shaft element being provided withsecond cam elements.

In one embodiment of the invention, the second, outermost, shaft elementmay have peripherally extending slots of limited angular extent throughwhich only the lobe portions of the first cam elements extend, saidsecond shaft element having means providing base circle cam surfaces forsaid lobe portions of the first cam elements. The first cam elements maybe of annular form and fit on entire circumferential regions of thefirst shaft element. The operative surface which is followed by afollower element engaged by the cam thus comprises the surface of thelobe portion of the first cam element, and a base circle region formedby the second shaft element or one or more additional elements connectedthereto.

The first cam elements may be made with a cylindrical internal bore,within which the first shaft element fits directly with a brazed orwelded or force-fitting connection provided between each cam element andthe shaft element. It will be appreciated in this case that it is onlythe lobe portion of each first cam element which can be moved angularlyrelative to the second shaft element; the base circle surface which isfollowed by a cam follower does not move.

If the second, outer, shaft element encloses the first shaft elementwith a small clearance therebetween, protuberances are needed in thesecond shaft element to accommodate the cam elements on the first shaftelement. In this case, these protuberances can themselves provide basecircle running surfaces for the cams, whose lobes are provided by thefirst cam elements on the inner shaft element. To ensure a smoothtransition from the base circles to the lobes, the protuberances can becontinued as web portions on the peripherally directed edges of theslots in the second shaft element.

If the second shaft element has a significantly larger diameter than thefirst shaft element, such that all but the lobes of the cam elements onthe first shaft element can be received within the normal diameter ofthe second shaft element, then annular members can be provided, securedto the external surface of the second shaft element adjacent theperipheral slots therein, to form the base circles of the operatingsurface of the first cams.

Preferably the first shaft element is a tubular body which extendsthroughout the cam shaft, and on which the first cam elements, ofannular configuration, are fixed. One suitable method of securing thecams is that of locally expanding the first shaft element within itscams, by hydraulic means. Laser welding, done from the inside of thetubular shaft element with the aid of a mirror is also a possible knowntechnique.

Alternatively, the first shaft element may be made up of individualsections joined together in the regions of the cam elements thereon bymethods such as above referred to. A cam element can be integrallyformed on each of such tubular sections.

The second, outer, shaft element must, in the case of a first shaftelement which has its cam elements fixed to it, comprise individualtubular sections joined to one another in the region of the peripheralslots therein. It is possible for two of the second cam elements to beintegral with a section of tube; this is also applicable in the case ofany bearing journals which may be provided, of larger diameter than thetube sections. The preferred method for joining the parts to one anotheris laser welding, the sections of tube being flush with one another.

Manufacture of such a cam shaft is done by placing individual tubularsections of the second shaft element on one another in the requiredsequence, e.g. by an assembly device. Any separate cam elements for thesecond shaft element would previously have been mounted on the tubesections. The first cam elements, for connection to the first shaftelement lying inside the second shaft element, would be placed in theperipheral slots in the second shaft element. The individual tubesections of the second shaft element can now be welded together. Any ofthe second cam elements not integral with individual tube sections maybe welded to the corresponding tube sections or secured thereto byhydraulic expansion of the relevant tube sections. After completion ofthe second shaft element, the first shaft element can be insertedaxially into the second shaft element and the first cam elementstherein. The first shaft element is then connected to the individualfirst cam elements after being suitably aligned, by welding or forcelocking by hydraulic expansion of the shaft element, as aforesaid. Ifthe second tube element requires to be expanded to accommodate the firstcam elements, this may be done by hydraulic expansion, in this case in adie, after which the peripheral slots through which the first camelements extend must be milled in the shaft element.

In known manner, an adjusting device may be provided at one end of thecam shaft for adjusting the angular relationship between the first andsecond shaft elements. The adjusting device may comprise an axiallymovable coupling element which is torsionally fast with one shaftelement and has torsionally-adjusting engagement with the other shaftelement, e.g. by a quick thread mechanism. For moving the couplingelement axially, an hydraulic cylinder device may be provided. One ofthe two shaft elements, preferably a second, outer, one, may be providedwith a driving pinion or pulley. Such an adjusting device may be omittedif each of the shaft elements has its own driving pinion or pulley, thedrive mechanisms of which are basically in synchronism with one anotherbut are adjustable with respect to the angular relationshiptherebetween.

In another embodiment, the second, outer, shaft element may comprise anumber of individual tubular sections connected to one another andhaving, at their points of connection to one another, part-tubularportions separated by longitudinally extending slots, said part-tubularportions extending through axial slots of limited angular extentprovided in the first cam elements. In this embodiment, the first camelements can enclose the first shaft element so as to provide a secureconnection, e.g. by a force fitting or welded or soldered connection.Preferably each first cam element has an annular inner portion and theaxial slots therein are radially spaced from the inside surface of suchinner portion, being spaced from one another by webs which support anouter portion of the cam element. This construction has the advantagethat the first cam element engages the first shaft element over anuninterrupted circumferential surface, for improved security. However,it is possible for the axial slots in each first cam element to openinto the interior aperture of the cam element, so that contact with thefirst shaft element is established over a number of circumferentiallyspaced webs only. In this case, the second shaft element need not haveits diameter increased where the first cam elements are provided.

The first shaft element may comprise a tubular body which extendsthroughout the cam shaft and on which the first cam elements are fixed,e.g. by hydraulic expansion or laser welding as above referred to.However, it is also possible for the first shaft element to compriseindividual sections joined together in the region of the cam elementsprovided thereon, as previously described. Once again, a cam element canbe integrally formed on each of such sections of the first shaftelement.

The second, outer, shaft element, which must comprise individuallongitudinal sections joined to one another in the case where the firstshaft element has its cam elements fixed to it, preferably has itssections joined to one another at the end of the part-tubular portionsthereof separated by the longitudinally extending slots. The second camelements can each be in one piece with one of the individual sections ofthe second shaft element. This is also the case for bearing journalswhere these are provided. Such bearing journals can be formed bysymmetrical expansion of the tubular material. Laser welding ispreferred as the method of joining the individual tubular sections toone another.

The two shaft elements may be arranged for their relative angularmovement such that they are radially guided relative to one another atleast at their ends and preferably in the region of any intermediatebearing journals. Provision may be made for a supply of lubricating oilhere.

This embodiment of cam shaft may be assembled in the following way. Ifthe second cam elements are not integral with the respective individualtubular sections of the second shaft element, they are to be connectedto the corresponding sections before they are joined to one another,e.g. by hydraulic expansion of the tubular sections. Following that, theindividual sections of the second shaft element are placed together inthe required sequence and at the same time the first cam elements arepositioned where they are joined, with the part-tubular portions of thesections extending through the axial slots in the first cam elements.The individual sections of the second shaft element are now able to bejoined together, for example by welding. After completion of this, thefirst shaft element can be inserted axially into the first cam elements,and connected thereto, after suitable alignment, for example byexpansion of the first shaft element by hydraulic pressure. Instead ofthe establishment of such a force fitting connection, laser welding maybe carried out from the inside of the tubular shaft element, with theaid of a mirror. This last named method could be done before connectionof the individual sections of the second shaft element to one another,but they should, however, firstly be firmly connected to the second camelements.

In known manner, an adjusting device may be provided at one end of thecam shaft, to cause a change in the position of the two shaft elementsrelative to one another, to alter the timing of the two groups of camelements relative to one another.

In a first embodiment, this change of position can occur in the form ofrelative angular movement between the two shaft elements. In this case,the axial slots in the first cam elements must have a circumferentialextent greater than that of the part-tubular portions of the secondshaft element which extend through them.

In a second embodiment, which could be combined with the first, arelative axial displacement of the shaft elements could be arranged tobe effected. In this case, the first and/or the second cam elementsshould have a cam form which changes axially as well ascircumferentially, and the lengths of the longitudinally extending slotsprovided between the part-tubular portions of the second shaft elementsections must be longer than the axial dimension of the first camelements having the axial slots.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described by way of example with reference tothe accompanying drawings, of which:

FIG. 1 is a longitudinal section through a first embodiment of cam shaftaccording to the invention;

FIG. 1A shows a section of the shaft of FIG. 1 along the line 1A--1A;

FIG. 1B is a view similar to FIG. 1A, with the shaft angularly shifted;

FIG. 1C is a section of the shaft of FIG. 1 along the line IC--IC;

FIG. 2 is a longitudinal section through a further embodiment of camshaft according to the invention;

FIG. 2A is a section along the line II--II of FIG. 3;

FIG. 3 is a transverse section through part of the cam shaft of FIG. 2;

FIG. 3A is a view similar to FIG. 3, with the shaft angularly shifted;

FIG. 4 is a transverse section showing a modification of the cam shaftof FIGS. 2 and 3; and

FIG. 4A is a view similar to FIG. 4, with the shaft angularly shifted.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring firstly to FIG. 1, the cam shaft there shown comprises a firsttubular shaft element 101 lying within a second tubular shaft element102. The first, inner, shaft element 101 extends throughout the lengthof the cam shaft, and has first cam elements 107 thereon, secured by anyof the means above described.

The second, outer, shaft element 102 comprises a number of individualtubular longitudinally extending sections joined to one another. Thesecomprise sections 103 which are each formed or provided with a camelement 108, sections 104 in each of which a peripherally extending slot109 is provided, and sections 105 which are each integrally formed witha tearing journal 106.

Each of the first cam elements 107 has a lobe portion 130 which extendsradially outwardly through the associated slot 109 in section 104. Wherethe slot 109 is provided, each section 104 is expanded to a protuberance110. If such expansion is carried out by internal hydraulic pressure,then the expansion must be performed before the slot 109 is cut, e.g. byuse of a milling cutter. The protuberance 110 continues as webs 112, 113adjacent where the lobe portions of the cam element 107 extend from theslot 109, to form a part of the cam track which is followed by a camfollower when the cam shaft is in use. Thus the protuberance 110 forms abase circle part of the cam track, whilst the webs 112, 113 formtransitional regions leading to the lobe portion of cam element 107.

The two shaft elements are movable angularly relative to one anotherabout the rotational axis of the shaft. An adjusting device is providedfor effecting such relative angular movement, the device being indicatedgenerally at 111. It comprises an inner body 116 which is connected tothe first shaft element 101, and an outer sleeve 117 connected to thesecond shaft element 102. A coupling element 118 is in engagement withexternal teeth 119 on the inner body 116, and with internal teeth 120 ofthe outer sleeve 117. One of the two sets of teeth 119, 120 comprisesaxial teeth, while the other comprises helical teeth. The couplingelement 118 is movable axially, being supported by a spring 121 relativeto the inner body 116 and being urgeable in the opposite direction,against the spring force, by a piston 122 movable in an hydrauliccylinder 123 and able to be subjected to pressure by an oil supply line124.

FIG. 2 shows another embodiment of cam shaft comprising a first, inner,shaft element 201 and a second, outer, shaft element 202. These twoshaft elements are able to be moved angularly and/or axially relative toone another about the axis of rotation of the cam shaft. An adjustingdevice for effecting such relative movement is not shown.

The second, outer, shaft element 202 comprises a number of individualtubular sections secured to one another. There are first sections 203,provided at their ends with longitudinal slots 209 leaving part-tubularportions therebetween, second sections 204 provided at their ends withlongitudinal slots 210 and symmetrical to the first sections, and athird section 205. Each of the sections 203, 204, 205 is supported by arespective bearing 206 within which runs a journal portion of thesection.

Where the sections 203, 204 are provided with their longitudinal slots209, 210, the sections are of increased diameter so that between theslots part cylindrical tubular portions 212, 213, 214, 215 remain,spaced from the first shaft element 201. The inner shaft element 201carries first cam elements 207 at these positions, and as most clearlyseen in FIG. 3 the part-tubular portions 212, 213 of the second shaftelement extend through axial slots 216, 217, 218, 219 in the camelements. The circumferential extent of each of the slots in the camelements is greater than the circumferential extent of each of thepart-cylindrical portions 212, 213, 214, 215 of the sections of thesecond shaft element, so that the first shaft element and first camelements thereon are able to move angularly relative to the second shaftelement through an angle indicated as α.

The sections of the second shaft element have second cam elements 208fixed thereon by any of the means aforesaid.

In FIG. 2, the first cam elements 207 are shown as three-dimensionalcams. The axial length of the slots 209, 210 is greater than thethickness (dimension in the axial direction) of the cam elements 207, sothat the first shaft element and cam elements thereon is also able tomove axially relative to the second shaft element and its cam elements.Whatever form of adjustment mechanism is provided at the end of the camshaft assembly should be able to provide this relative movement as wellas the angular movement as above described.

Also shown in FIG. 2 is the provision in the sections of the secondshaft element of oil holes 211 in the region of the bearings 206. Theoil supply for such bearings also provides for lubrication of the shaftelements for their movement relative to one another.

In FIG. 3 the illustrated form of the first cam element 207 has acomplete annular inner portion separated by webs from an outer portionof the cam element. This provides a large contact area with the firstshaft element 201. In the cam element 207 shown in FIG. 4, there is nosuch annular inner portion; the outer surface of the inner shaft element201 is engaged by webs provided between axial slots 224, 225, 226, 227which extend through the cam element and in which the part-tubularportions 220, 221, 222, 223 of the section of the outer shaft elementextend. Again a circumferential clearance is shown between the portionsof the shaft section and the slots in the cam element, to permitrelative movement through an angle α therebetween. In this embodiment,the section of the outer shaft element need not be expanded to provide aclearance from the inner shaft element.

If the two shaft elements are able to move axially relative to oneanother, they need not be angularly relatively movable. This causes therotational rigidity of the second shaft element 202 to increase, thelatter being able to derive some support from the elements provided onthe first shaft element.

We claim:
 1. A cam shaft for valve operation in an internal combustionengine, comprising:a first cam shaft element; a second shaft element,said first shaft element being disposed within said second shaft elementand being angularly movable relative thereto; first cam elementsprovided on said first shaft element, said first cam elements includinglobe portions; slots provided in said second shaft element through whichat least said lobe portions of said first cam elements extend; andsecond cam elements provided on said second shaft element, said slots insaid second shaft element extending peripherally to a limited angularextent and only the lobe portions of the first cam elements extendingtherethrough, said second shaft element having means providing basecircle cam surfaces for said lobe portions of the first cam elements. 2.A cam shaft according to claim 1 wherein said means comprisesprotuberances formed in the second shaft element.
 3. A cam shaftaccording to claim 1 wherein said first cam elements comprise annularelements individually fixed on the first shaft element.
 4. A cam shaftaccording to claim 3 wherein said first shaft element comprises atubular body which extends throughout the cam shaft.
 5. A cam shaftaccording to claim 1 wherein said first shaft element comprisesindividual tubular sections connected to one another in the region ofthe first cam elements.
 6. A cam shaft according to claim 5 wherein eachof said first cam elements is formed integrally with one of saidsections of the first shaft element.
 7. A cam shaft according to claim 1wherein said first cam elements have a force-fitting connection to thefirst shaft element.
 8. A cam shaft according to claim 1 wherein thefirst cam elements have a welded or brazed connection to the first shaftelement.
 9. A cam shaft according to claim 1 wherein said second shaftelement comprises a number of individual tubular sections joined to oneanother.
 10. A cam shaft according to claim 9 wherein said second camelements are integral with said tubular sections of the second shaftelement.
 11. A cam shaft according to claim 9 wherein bearing journalsare integral with said tubular sections of the second shaft element. 12.A cam shaft according to claim 9 wherein said tubular sections of thesecond shaft element are welded flush with one another.
 13. A cam shaftaccording to claim 1 further comprising an adjusting device at one endof the cam shaft, torsionally fast with one shaft element and havingtorsionally-adjusting engagement with the other shaft element.
 14. A camshaft according to claim 1 wherein said second shaft element comprises anumber of individual tubular sections connected to one another andhaving, at their points of connection to one another, part-tubularportions separated by longitudinally extending slots, said part-tubularportions extending through axial slots of limited angular extentprovided in said first cam elements.
 15. A cam shaft according to claim14 wherein said part-tubular portions of said sections of the secondshaft element fit over the adjacent tubular section.
 16. A cam shaftaccording to claim 14 wherein each of said tubular sections of thesecond shaft element comprises two of said part-tubular portionsextending through the axial slots in the first cam elements.
 17. A camshaft according to claim 14 wherein said axial slots in the first camelements are radially spaced from an internal surface of an innerportion thereof.
 18. A cam shaft according to claim 14 wherein saidaxial slots in the first cam elements open into interior aperturesthereof.
 19. A cam shaft according to claim 14 wherein said first shaftelement comprises a tubular body extending throughout the cam shaft. 20.A cam shaft according to claim 14 wherein said first shaft elementcomprises individual sections joined together in the region of the camelements provided thereon.
 21. A cam shaft according to claim 14 whereina first cam element is integral with each of said sections of the firstshaft element.
 22. A cam shaft according to claim 14 wherein said firstcam elements are connected to the first shaft element by force fittingor welding or brazing.
 23. A cam shaft according to claim 14 whereinsaid second cam elements are connected to the second shaft element byforce fitting or welding or brazing.
 24. A cam shaft according to claim14 wherein said second cam elements are integral with said sections ofthe second shaft element.
 25. A cam shaft according to claim 14 whereinbearing journals are integral with said sections of the second shaftelement.
 26. A cam shaft according to claim 14 wherein said sections ofthe second shaft element are connected to one another by force fitting,welding or brazing.
 27. A cam shaft according to claim 14 wherein saidaxial slots in the first cam elements have a circumferential extentgreater than that of the part-tubular portions of the second shaftelement which extend through them, and an adjusting device is providedfor effecting relative angular movement between the two shaft elements.28. A cam shaft according to claim 14 wherein cam elements on one of theshaft elements have a cam form which changes axially as well ascircumferentially, and wherein an adjusting device is provided foreffecting relative axial movement between the two shaft elements.